Mean velocity and turbulence measurements of supersonic jets with fluidic inserts

The noise produced by the supersonic, high temperature jets that exhaust from military aircraft is becoming a hazard to naval personnel and a disturbance to communities near military bases. Fluidic inserts have been developed for noise reduction using distributed nozzle blowing. Fluidic inserts are created that simulate mechanical, hardwall corrugations, while having the advantage of being an on demand noise reduction method. This research focuses on detailed measurements of the flow field modifications created by the hardwalled and fluidic corrugations to better understand how each produces noise reduction of the jet. Unsteady velocity measurements using a Laser Doppler Velocimeter are performed on jets exhausting from nozzles with fluidic inserts and hardwall corrugations. Measured mean axial velocity and axial turbulence intensity are examined to illuminate the differences in the flow field from jets with fluidic inserts. Comparisons of laser Doppler measurements with RANS CFD simulations are shown with good agreement. The fluidic inserts produce less velocity deficit but more turbulence in the near exit region of the jet. After one jet diameter the mean flows are nearly identical, but the turbulent levels behind the fluidic inserts continue to be slightly higher than behind the hardwall corrugations.